style: switch accent from Gruvbox blue to Gruvbox yellow; fix Tended layout

- Replace accent palette (#076678 blue → #b57614 yellow light,
  #83a598 green → #fabd2f yellow dark) across config, critical CSS,
  pagefind overrides, and all hardcoded hex references
- Stack post meta rows (Planted / Tended) vertically via flex-col

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

_includes/layouts/post.njk

@@ -27,7 +27,7 @@ withBlogSidebar: true
   </div>
   {% endif %}
 
-  <div class="post-meta mb-4 sm:mb-6">
+  <div class="post-meta mb-4 sm:mb-6 flex flex-col gap-1">
     <div class="flex flex-wrap items-center gap-2">
       <span class="font-mono text-sm">Planted: </span><time-difference><time class="dt-published font-mono text-sm" datetime="{{ date.toISOString() }}">
         {{ date | dateDisplay }}